Impact of COVID-19 pandemic on the dynamic of patients with oral and maxillofacial trauma: interrupted time-series analysis

Oral and maxillofacial trauma is influenced by various factors, including regional characteristics and social background. Due to the coronavirus disease 2019 (COVID-19) pandemic, a state of emergency was declared in Japan in March 2020. In this study, we aimed to examine the dynamics of patients with oral and maxillofacial trauma over a 12-years period using interrupted time-series (ITS) analysis. Patients were examined at the Shimane University Hospital, Maxillofacial Trauma Center from April 2012 to April 2023. In addition to general patient characteristics, data regarding the type of trauma and its treatment were obtained from 1203 patients (770 men and 433 women). Group comparisons showed significant differences in age, trauma status, method of treatment, referral source, route, and injury occasion. ITS analysis indicated significant changes in combined nasal fractures, non-invasive reduction, and sports injuries (P < 0.05), suggesting COVID-19 significantly impacted oral and maxillofacial trauma dynamics. A pandemic of an infectious disease may decrease the number of minor trauma cases but increase the number of injuries from outdoor activities, resulting in no overall change in the dynamics of the number of trauma patients. Medical systems for oral and maxillofacial trauma should be in place at all times, independent of infectious disease pandemics.


Background data
Data collected from the electronic medical records included the following: age (years), sex (male/female).

Statistical analysis
For patient background factors, continuous variables were checked for normality using the Shapiro-Wilk test.Descriptive statistics were expressed as the mean (standard deviation) and number of cases (%).Group comparisons were performed between two groups, before and after the COVID-19 pandemic, and t-tests or chi-square tests were performed depending on the type of variable.Interrupted time series analysis was employed to analyze the impact of the COVID-19 pandemic on patient dynamics in patients with oral and maxillofacial trauma 19 .Generally, interrupted time series analysis is the preferred analysis method as a robust quasi-experimental approach in the absence of a control group.Interrupted time series studies have shown that split regression analysis is effective in estimating intervention effects.In this study, the dependent variable Y was the item with significant differences in between-group comparisons, and the model for the number of occurrences per month was constructed as follows: where Y represents the number of cases, and time denotes the number of cases per month from April 2012 to April 2023.Z is a variable set to 0 before the COVID-19 pandemic (until April 15, 2019) and to 1 after the COVID-19 pandemic (after April 16, 2019), and the last variable is the product of Z and time.Since we aimed to reflecting the change in trend (change in slope) due to the COVID-19 pandemic, we considered the shift in patient dynamics when Z ij Time ij had a significant probability of P < 0.05.One of the greatest strengths of interrupted timeseries studies is their intuitive graphical presentation of results.The visual inspection of the series over time is the first step in analyzing time series data.Such an analysis enables the examination of whether the time trend changed in dynamics before and after an intervention (in this study, a novel coronavirus pandemic).Additionally, Poisson regression analysis was used to create the model since the data were counts of rare events.Statistical analysis was performed using SPSS (version 27; SPSS IBM Corp., Armonk, NY, USA).Two-tailed P-values were calculated for all analyses, with an alpha level of significance set at 0.05.

Patient characteristics
The data was collected from 1203 patients, including 770 (64.0%) males and 433 (36.0%) females, with a mean age of 39.5 years (standard deviation, 30.7).The most frequent traumatic conditions were tooth injury (n = 229, 19.0%), followed by mucosa laceration (n = 219, 18.2%) and zygoma and zygomatic arch fractures (n = 125, 10.4%).Among treatment methods, open reduction and rigid fixation was performed in 337 (28.0%) patients, and 332 (27.6%) patients received wound treatment.Referrals from an Emergency and Critical Care Center/ Advanced Trauma Center accounted for 928 (77.1%) patients, and 826 (68.7%) patients were referred on foot as the method of hospital visit.Slip down was the leading cause of injury, with 593 (49.3%) cases.The patient background characteristics are presented in Table 1.

Comparison between groups before and after the pandemic
Significant differences were observed in age.Regarding trauma status, significant differences were observed among laceration cases, including nasal bone, orbital wall, zygomatic bone, and zygomatic arch fracture cases.A significant difference was observed in close reduction (including nasal bone reduction) in treating fracture cases, as well as in tooth extraction and wound care among non-fracture patients.Regarding the referral origin, a significant difference was observed in dental/medical clinic and Emergency and Critical Care Center/Advanced Trauma Centers.The mode of transportation to the hospital showed significant differences in ambulance and doctor helicopter usage.Trauma status displayed a significant difference among laceration cases.The cause of injury was significantly different among sports, traffic accidents, and work-related accidents.Details of the group comparisons are presented in Table 2. (1)

Changes in patient dynamics before and after the pandemic based on interrupted time series analysis
The split time series analysis revealed no significant change in the overall number of patients; however, significant dynamic changes were found in nasal bone fracture cases, close reduction (including nasal bone reduction) for maxillofacial fracture patients, and sports as the cause of injury (Fig. 1 and Table 3).

Discussion
This study was conducted in a level 1 trauma center in a super-aged community, as previously mentioned, and the data were collected during an "emergency declaration, " a Japanese governmental policy that did not require a mandatory lockdown, which should be considered, given that regional characteristics have a particular impact on this study.The major finding of this study is divided into three parts.First, the COVID-19 pandemic altered the trend in the number of cases of nasal bone fractures.Nasal bone fractures can result from various causes, including traffic accidents, falls, sports, and violence.A study in Turkey reported a decrease in the number of nasal bone fracture cases during the COVID-19 pandemic compared with the previous year 20 .This aligns with the simple comparison performed in our study, which also indicated an increased percentage during the pandemic, but a decline in dynamics over time.In contrast to the Turkish study, which noted an increase in assault as the cause of nasal bone fractures, our study did not show a similar trend.A meta-analysis on the association between violence and stay-at-home/confinement orders found an increase in incidents of violence, including domestic violence, in response to stay-at-home/confinement orders.Similar results were reported in multiple studies worldwide, making an increase in violence as a cause of nasal bone fractures more plausible 21 .This discrepancy may stem from differences in the extent of the stay-at-home/confinement orders or lockdowns in Japan.Unlike many countries that implemented enforceable lockdowns at the beginning of the COVID-19 pandemic to control the spread of the disease, the Japanese government issued a non-enforceable declaration of a state of emergency.While the declaration of a state of emergency in Japan is believed to have effectively prevented people from going out to high-risk destinations during the pandemic, prolonged declaration of a state of emergency led people to return to their pre-pandemic lifestyle 22 .This dynamic change may be due to sports trauma, but the behavioral restrictions associated with the pandemic may also have contributed to increased frailty and locomotive syndrome in the elderly, leading to an increase in falls 23 .Thus, the declaration of emergency may not have been as coercive as a lockdown, potentially explaining the absence of an increase in violence-related nasal bone fractures.
Second, closed reduction (including nasal bone reduction) mirrored the dynamics of nasal fractures, with an increase in percentage but undergoing a change in trend as a temporal dynamic.A report from the United States reported that during the COVID-19 pandemic, the clinical characteristics of patients with facial fractures remained unchanged, but the use of mandibulomaxillary fixation (MMF), a conservative treatment for mandibular fractures, decreased significantly 24 .However, the cause of the MMF decrease is considered to differ from the change in the dynamics of closed reduction (including nasal bone reduction) in Japan.The authors suggest that the decrease in MMF usage was due to the risk of being unable to perform emergency intubation if COVID-19 disease developed after MMF 25 .In India, all oral and maxillofacial trauma cases were reportedly treated exclusively with closed reduction (including nasal bone reduction) for 6 months after the lockdown 26 .However, at our hospital, the study facility, no situation occurred where the treatment method was changed to closed reduction (including nasal bone reduction) due to the emergency declaration or COVID-19 pandemic.No nosocomial infection occurred among patients or medical staff since the usual treatment method was selected as the first choice.This is inferred as a factor that differs from both India and other countries.Although fully explain the mechanism underlying the results of this study is challenging due to the limited number of previous reports, it is at least possible that the weakly binding restrictions imposed by the declaration of a state of emergency, which were weaker than those of a lockdown, may influence the implemented treatment methods.Simultaneously, these less restrictive laws and regulations may influence the prioritization of medical decisions.Meanwhile, it was suggested that a weakly binding statute might allow for a flexible response that prioritizes medical judgment 27 .The third point, regarding sports as a cause of oral and maxillofacial trauma, suggests that this phenomenon may be unique to Japan.An article on lockdowns and sports trauma in children noted that sports trauma cases were almost completely absent during the lockdown period 28 .A significant decrease in sports-related trauma during a lockdown was also reported in adults 29 .While many papers attribute the reduction in human contact during a lockdown as a factor, Japan showed an increasing dynamic after the declaration of the state of emergency, despite a decrease in percentage.This was attributed to the emergency declaration, in addition to the request of minimizing opportunities for human contact, by avoiding closed, enclosed, and crowded places.This encouraged the elderly to stay indoors, whereas children increased their outdoor activities to reduce the infection risk 30 .
To summarize the three major findings of this study, behavioral restrictions in society may change the lifestyle of individuals, thereby altering the profile of oral and maxillofacial trauma.This result is consistent with that of other reports related to oral and maxillofacial injuries and traumas 31,32 .On the other hand, the fact that the dynamics of the number of oral and maxillofacial trauma cases, including both minor and severe, advanced trauma cases, did not change indicates that oral and maxillofacial surgeons need to maintain the regular healthcare system, even in the event of an acute infectious disease pandemic, because patient needs in oral and maxillofacial trauma care might not change.
A minor finding of this study is that overall oral and maxillofacial trauma cases in Japan were unaffected by the emergency declaration and did not exhibit dynamic changes.Although a strong legally binding lockdown may reduce the risk of emergency room visits, notably in oral and maxillofacial trauma, injuries may increase due to other factors such as increased domestic violence 33 .Therefore, it was deemed that oral and maxillofacial trauma care provided under a declared state of emergency during a pandemic would be better served by maintaining the same medical system and treatment plans as those under normal circumstances.
This study has two limitations.First, it used 10 years of data in the split time series analysis, which assumes that medical standards and systems remained similar during this period.Although in reality, changes may have occurred that were not observed in the data.Second, the region providing data for this study is characterized as a super-aged society in a mountainous area in Japan, potentially limiting the generalizability of the results Table 3. Changes in patient dynamics before and after the pandemic based on interrupted time series analysis.β: coefficient, Z: a dummy variable indicating the before (coded 0) or after period (coded 1), *P < 0.05.

Figure 1 .
Figure 1.Number of cases over time by stratification.(a) Total number of traumatic cases; (b) nasal cases; (c) number of closed reductions (including nasal bone reduction) in fracture patients; and (d) number of sportsrelated injuries.